The present invention relates to flow control devices, and relates more particularly to constant-flow devices for regulating a fluid flow to a substantially constant flow rate over a range of pressure differentials.
In many fluid systems there is a desire to regulate the fluid flow to a substantially constant volumetric flow rate over a range of pressure differentials. Most constant-flow valves are designed to provide a substantially constant flow rate of fluid flowing in one direction through the valve, but are not equipped to regulate fluid flow in an opposite direction to a constant flow rate.
In a heat exchanger system for alternatively heating and cooling, the required fluid flow rates are generally determined by the differential temperature that is available and the thermal energy transfer required. For example, secondary refrigeration systems, also known as hydronic systems, typically provide chilled water for cooling and heated water for heating. The chilled water typically is supplied at about 20 degrees F. lower than the desired final temperature, and the heated water is typically supplied at 60 to 100 degrees F. higher than the desired final temperature. As a result, the chilled water flow rate generally must be about three to five times that of the heated water flow rate. This difference in flow rates is not an issue when separate cooling and heating heat exchangers are used on separate cooling and heating fluid circuits; two separate uni-directional constant-flow valves are simply used in the two separate fluid circuits to achieve the required different flow rates for heating and cooling. However, it would be desirable to simplify the system by using a single heat exchanger connected to the separate fluid circuits for both cooling and heating. In that case, it would be desirable to have a single flow-control device that could regulate the flow to a first flow rate in one flow direction for cooling and to a second flow rate in the opposite direction for heating.
The present invention addresses the above problem and achieves other advantages by providing a flow control device capable of regulating a fluid flow to a substantially constant volumetric flow rate whether the fluid flows in one direction or in the opposite direction through the device. The flow rate in the one direction can be the same as or different from the flow rate in the opposite direction, yet the device is particularly simple in construction.
In accordance with a first aspect of the invention, a bi-directional flow-control device includes a housing defining a flow passage therethrough, and first and second orifices formed separately from the housing and installed in the passage thereof, each orifice being tubular and having a seat defined at one end, each seat having a plurality of flow-control channels extending transversely therein and spaced apart circumferentially, the seat of the second orifice being axially spaced from and facing the seat of the first orifice. A resiliently deformable diaphragm is disposed in the passage between the seats of the orifices, whereby flow through the passage in a first direction urges the diaphragm against the seat of the first orifice and flow through the passage in an opposite second direction urges the diaphragm against the seat of the second orifice, the diaphragm in each case deforming into the channels in the seat to varying degrees as a function of pressure differential across the diaphragm such that in either flow direction the flow is regulated to a substantially constant volumetric flow rate over a range of pressure differentials.
The diaphragm is held in a generally coaxial alignment with the seats of the orifices by a cage arrangement formed separately from the housing and installed in the flow passage between the seats. In one embodiment, the cage can comprise first and second spiders joined with the first and second orifices, respectively. Each spider comprises a plurality of circumferentially spaced, axially extending legs each having a fixed end joined to the respective orifice and extending toward the other orifice and terminating in a free end. The spiders allow the diaphragm to float freely between the seats of the orifices. The legs of the first spider are circumferentially spaced from and axially overlap with the legs of the second spider. Each orifice and its associated spider preferably comprise a one-piece molded structure. The structure can be molded of a substantially rigid resin composition. In another embodiment, the cage comprises a generally tubular structure formed separately from the orifices and having legs that project radially for centering the diaphragm in the flow passage.
The flow-control channels in the first orifice seat can be configured substantially differently from the channels in the second orifice seat so that the volumetric rate of flow in one direction through the device is substantially different from the rate of flow in the opposite direction. Preferably, the diaphragm is symmetric such that its opposite sides that engage the seats are identical, thereby allowing the diaphragm to be installed in one orientation or an opposite orientation without affecting the performance of the device.
In accordance with another aspect of the invention, a bi-directional flow-control device comprises a housing having a passage and first and second orifices and a diaphragm generally as noted above. The first orifice is inserted axially into the passage so as to be coaxial with the passage, and a first retainer is inserted axially into the passage from one end thereof and fixed therein to prevent the first orifice from moving axially toward the one end of the passage. The second orifice is likewise inserted axially into the passage and a second retainer is inserted axially into the passage from the opposite end thereof and fixed in the passage to prevent the second orifice from moving axially toward the opposite end of the passage. The retainers preferably comprise generally disk-shaped members inserted into the passage such that outer peripheries of the retainers frictionally engage the inner surface of the passage to fix the retainers in place axially in the passage. The retainers have flow passages therein to allow fluid to flow through them.